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How do I know what size airplane to go with motor

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How do I know what size airplane to go with motor

Old 05-05-2021, 06:22 AM
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Default How do I know what size airplane to go with motor

How do I know what size airplane or what weight airplane will work with a 1100 KV 40 amp motor brushless motor?
Old 05-06-2021, 08:12 AM
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A motor with velocity konstant Kv (property) of1100rpm/volt (unit) can be the motor in your toothbrush, but it can also be the motor of a French 1:1 high-speed TGV train.
Kv, in combination with voltage, only tells you how fast the motor wants to run, it does not tell you if it can run that fast. That's what power is all about, ability.
So we need to know the power (property) of the motor as well, measured/expressed in watt (unit).

Below an excellent quote about motor and plane selection. You can reverse the magic numbers, to give you a range of plane masses.
brushless motors Kv?.
Originally Posted by scirocco
While an absolutely critical part of the system ...
... Kv is actually the item one should choose last.
  1. Decide your peak power requirement based on the weight of the model and how you want to fly it:
    Magic numbers for modellers.
  2. Pick a preferred cell count (voltage) and pack capacity for how to deliver the power.
  3. Pick a prop that will a) fit on the model and b) fly the model how you want - often as big as will fit is a good choice, but if high speed is the goal, a smaller diameter higher pitch prop will be more appropriate.
  4. Look for a size class of motors that will handle the peak power - a very conservative guide is to allow 1 gram motor weight for every 3 watts peak power.
  5. Then, look for a motor in that weight range that has the Kv to achieve the power desired with the props you can use - a calculator such as eCalc allows very quick trial and error zooming in on a decent choice. For a desired power and prop, you'd need higher Kv if using a 3 cell pack compared to a 4 cell pack. Or for a desired power and cell count, you'd need higher Kv if driving a smaller diameter high speed prop compared to a larger prop for a slow model.
The reason I suggest picking Kv last, is that prop choices have bounds - the diameter that will physically fit and the minimum size that can absorb the power you want. On the other hand, combinations of voltage and Kv are much less constrained - at least before you purchase the components.

So Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, e.g. limited prop diameter, if it's a pusher configuration, or if you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS

Last edited by ron_van_sommeren; 05-06-2021 at 08:16 AM.
Old 05-07-2021, 12:10 PM
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Thank you for all the information I'm sorry to have to tell you that at this point in my development it's a little bit over my head even though I'm not a young man I just found a set of motor and ESC and props and so on so forth but no receiver online for a cheap price and thought I could find some kind of a kid to build for it but it's too much money as it turns out so I'm not going to do it anyway so I guess you can move point now no point I said moot point the speech recognition really stinks I can't afford this hobby

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